Just starting to heavily work-out vs. what to eat?

I'm not really sure as to what to be eating. I went shopping and got protien bars, some steaks, and a lot of vitamin water. I also got some protien shake powder. I would just like some help. I am like 5'9 143 and have a pretty athletic body (muscular but not huge) I have never been fat in my life and it is hard for me to gain wieght, so I am unsure as to what to eat to gain wieght in muscle. Any tips would be appreciated. thanks

eat eat eat. You might think you're eating alot, but take whatever you're eating now and eat more, that is how you gain weight. I am a big fan of chicken breast and tuna, lean meats are my thing, I stay away from red meat for multiple reasons mostly. Eggs are great, I would get some cottage cheese and yogurt (ibdairyhaters) and good breads, cheeses and lunch meats. Those are my favorite foods I'm finding for trying to bulk (or cut).